Not Applicable.
Not Applicable.
Not Applicable.
The present invention relates to valves of the type that control pressure to a hydraulically actuated device by means of venting to a sump or exhaust a portion of the fluid in a control pressure chamber from a supply of pressurized fluid. Valves of this general configuration are known in the art and are typically electrically controlled by an electromagnetic solenoid which moves a valve member connected to the armature of the solenoid in response to variable current flow in the solenoid coil.
It is often desired to provide a fluid pressure control signal to a control signal port or outlet provided in the control signal pressure chamber for controlling a hydraulically actuated device. Ideally, as the coil current is increased the pressure in the control signal port is either proportionately increased or proportionately decreased depending upon whether the valve is of the normally closed or normally open arrangement with respect to the supply pressure to the control signal pressure chamber.
However, where a relatively low control signal pressure and thus a low flow is desired for operating the hydraulically actuated device, it has been found that the pressure response of the valve with respect to the electrical current flow in the solenoid does not produce a proportional response. Thus, electrical control of the hydraulic actuated device at low levels has proven to be quite difficult; and, the results have been unacceptable where precision control of the hydraulically actuated device is required, as for example, in the shift control devices in power transmissions, particularly for automatic transmissions used in motor vehicles.
Thus, it has been desired to provide an electrically operated pressure control valve for controlling flow of hydraulic fluid to an hydraulically actuated device and to provide linearly proportional control over the full range of energization current to the valve such as, for example, a solenoid operated valve.
The present invention provides a solenoid operated valve which provides flow from a pressure supply inlet to a control signal pressure chamber and a control signal outlet port from the chamber by means of controlling the flow from the inlet to the control signal chamber and by bleeding fluid from the control pressure signal chamber and controlling flow to an exhaust outlet or port from the signal chamber.
The valve of the present invention utilizes a poppet-type valve connected to the solenoid armature for closing and opening against a valve seat formed in the control pressure signal chamber; and, the poppet valve effect is disposed to movement of a spool valve which controls flow from the supply inlet to the control pressure signal chamber.
In one embodiment of the invention, with the solenoid de-energized the exhaust poppet is in the closed position and the spool valve is in the open position with respect to the supply inlet and provides proportional bleeding of exhaust flow and reduction of the inlet flow with increasing solenoid energization current. In the preferred form of the normally open valve, the spool valve closing of the supply inlet is delayed until the coil is energized in the range of about Eighty to One Hundred Percent (80-100%) of maximum coil current, thereby permitting the bleed flow to the exhaust to provide more accurate proportional flow control in the valve as the spool nears closure of the supply inlet.
In another embodiment of the invention in the solenoid de-energized condition the supply inlet port to the control pressure chamber is closed by the spool; and, the poppet valve controlling flow to the exhaust port from the control pressure signal chamber is open. As the solenoid is progressively energized from Zero to One Hundred Percent (0-100%) of maximum current, the inlet is progressively opened and the exhaust progressively closed in a manner providing pressure to the control signal outlet which is proportional to coil energization. In the presently preferred practice, the movement of the spool to open the pressure inlet is delayed until the coil is energized in the range of about Five to Twenty Percent (5-20%) of maximum current.
The present invention thus provides a solenoid operated pressure bleed type hydraulic fluid control valve which exhibits linear proportional control characteristics over the complete range of coil energization from Zero to One Hundred Percent (0-100%) of maximum current.